Glass substrate for a magnetic disk, magnetic disk and method of manufacturing a magnetic disk

ABSTRACT

A glass substrate for a magnetic disk, wherein, in regions with respect to two places arbitrarily selected on a surface of the glass substrate on its central portion side relative to its outer peripheral end, a surface shape with a shape wavelength in a band of 60 to 500 μm is extracted from surface shapes in each of the regions and, assuming that a root mean square roughness Rq of the surface shape is given as a microwaviness Rq, the difference between the microwavinesses Rq of the regions is 0.02 nm or less or the difference between standard deviations of the microwavinesses Rq of the regions is 0.04 nm or less.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 12/810,782 filed Jun. 25,2010, which is a U.S. National Phase Application under 35 U.S.C. §371 ofInternational Patent Application No. PCT/JP2008/073418 filed Dec. 24,2008, which claims the benefit of Japanese Application No. 2007-338966,filed Dec. 28, 2007, and Japanese Application No. 2007-338967 filed Dec.28, 2007, all of which are incorporated by reference herein.

TECHNICAL FIELD

This invention relates to a glass substrate for a magnetic disk thatenables high-density recording and reproduction, to the magnetic disk,and to a method of manufacturing the magnetic disk.

BACKGROUND ART

As one of information recording media adapted to be mounted ininformation storage devices, there is known a magnetic disk adapted tobe mounted in a hard disk (HDD). In recent years, it is stronglyrequired to improve the recording capacity of the magnetic disk and thusit is of urgent necessity to increase the recording density thereof andto extend the recording area thereof.

As a factor for enabling high-density recording, it is necessary toreduce as much as possible the flying height of a magnetic head withrespect to the magnetic disk and, for that purpose, it is necessary tomake smoother a surface of the magnetic disk.

In order to extend the recording area, it is necessary to ensure aslarge as possible a smooth region of the main surface. However,depending on polishing conditions of a glass substrate, a surface-downin which a surface is lowered relative to a main surface of the glasssubstrate or a surface-up (hereinafter referred to as a rise) relativeto the main surface occurs at an outer peripheral end portion of thesubstrate. When the magnetic head flies over the magnetic disk havingsuch a shape, the head may be inclined at the surface-down or riseportion to make its flight unstable, thus causing a crash. Thesurface-down or rise portion has been impeding the extension of therecording area.

In recent years, there have been actively developed a magnetic headattached with a pad for preventing adhesion of the magnetic head even ifa magnetic disk is smooth and a LUL (Load/Unload) system that enablesrealization of a lower flying height. Normally, in the case of this LULsystem, a surface of a magnetic disk is smooth and, while the magneticdisk is stopped, a magnetic head stands by on the outside of themagnetic disk and, after the magnetic disk starts rotation, the magnetichead moves from the outside of the disk and flies over the surface ofthe disk to perform recording/reproduction. Therefore, in general, alower flight is achieved as compared with the CSS system. In the case ofthe LUL system, in order to ensure the flying stability of the magnetichead, it is necessary to control an outer peripheral end portion shapeof a substrate more strictly than in the case of the CSS system. In thecase of the LUL system, since the low flight of the head is enabled,higher-density recording is made possible as compared with the CSSsystem.

In view of this, in order to realize a low flight of a magnetic head inthe LUL system, there is an invention that achieves a smoothness highenough for enabling high-density recording and specifies an outerperipheral end portion shape to a predetermined value (e.g. specifying asurface-down in which a surface is lowered relative to a main surface ofa glass substrate, or the like) for enabling extension of a recordingarea to the periphery (JP-A-2004-265582 (Patent Document 1)).

-   Patent Document 1: JP-A-2004-265582

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

However, a problem has arisen that even if the outer peripheral endportion shape of the glass substrate is improved by high-precisionpolishing or the like, i.e. even if a surface-down in which a surface islowered relative to the main surface of the glass substrate or asurface-up (rise) relative to the main surface is reduced, when themagnetic head flies over a magnetic disk having such a shape, the flightof the head becomes unstable so that the flying height of the magnetichead cannot be lowered. This will be explained in detail hereinbelow.

First, for example, as shown in FIG. 5, in the case of a glass substratefor a magnetic disk with a diameter of 65 mmφ (radius 32.5 mm), as anindex of an outer peripheral end portion shape (an index representingthe flatness of an outer peripheral end portion shape in the range of±μm with respect to a main surface as a reference plane (zero)) of theglass substrate, use is made of a larger value of maximum distances band c in positive and negative directions, respectively, within therange of a straight line a connecting between two points, i.e. a point Aat radius r=29.9 mm and a point B at radius r=31.5 mm from the center ofthe substrate, and this value is called (defined as) Duboff.

In the conventional case where Duboff was greater than 30 nm, it waspossible to reduce the touch-down height (TDH) at an outer peripheralend portion position as Duboff was reduced. On the other hand, in thepresent case where Duboff was 30 nm or less, as a result of examiningthe relationship between Duboff and the touch-down height (TDH) at anouter peripheral end portion position (position at radius r 31.5 mm), nocorrelation was observed as shown in FIG. 15. That is, it was seen thateven if the outer peripheral end portion shape of the glass substratewas improved, i.e. even if a surface-down in which a surface was loweredrelative to the main surface of the glass substrate or a surface-up(rise) relative to the main surface was reduced, it was not possible toreduce the touch-down height (TDH) at its outer peripheral end portionposition (variation in touch-down height largely appeared).

Next, in the conventional case where the average value of themicrowaviness (MW-Rq) (definition and so on will be described later)over the entire surface of a substrate was greater than 4 Å, it waspossible to reduce the touch-down height (TDH) at its outer peripheralend portion position by reducing the average value of the microwaviness(MW-Rq) over the entire surface of the substrate or by reducing themicrowaviness (MW-Rq) at its outer peripheral end portion assuming thatinner peripheral TDH<outer peripheral TDH. On the other hand, in thepresent case where the average value of the microwaviness (MW-Rq) overthe entire surface of a substrate was 4 Å (0.4 nm) or less, as a resultof examining the relationship between the microwaviness (MW-Rq) at itsouter peripheral end portion position (position at radius r 31.5 mm) andthe touch-down height (TDH) at its outer peripheral end portion position(position at radius r 31.5 mm), no correlation was observed as shown inFIG. 16. That is, it was seen that even if the microwaviness wasimproved (reduced) at the outer peripheral end portion of the glasssubstrate, it was not possible to reduce the touch-down height (TDH) atits outer peripheral end portion position (variation in touch-downheight largely appeared).

It is an object of this invention to devise means for solving theabove-mentioned problem.

Means for Solving the Problem

As a result of examining its cause, the present inventors have foundthat when two regions are arbitrarily selected on a surface of a glasssubstrate and unless the difference or ratio between microwavinesses(definition and so on will be described later) measured in therespective regions satisfies a certain predetermined relationship, it isnot possible to realize a reduction in flying height of a magnetic head.

Specifically, for example, as shown in FIG. 7, the relationship betweenthe difference (radial direction MW-Rq (OD-MD): measured in a wavelengthband of 60 to 500 μm) between a microwaviness at an outer peripheral endportion (e.g. a position at radius r=31.5 mm±0.05 mm) and amicrowaviness at a central portion (e.g. a position at radius r=25 mm±3mm) and the touch-down height (TDH) was examined and, as a result, astrong correlation was observed. That is, it was seen that it waspossible to reduce the touch-down height (TDH) at the outer peripheralend portion position by reducing the difference (radial direction MW-Rq(OD-MD)) between the microwaviness at the outer peripheral end portionand the microwaviness at the central portion.

Further, for example, as shown in FIG. 8, the relationship between theratio (radial direction MW-Rq (OD/MD): measured in a wavelength band of60 to 500 μm) between a microwaviness at an outer peripheral end portion(e.g. a position at radius r=31.5 mm±0.05 mm) and a microwaviness at acentral portion (e.g. a position at radius r=25 mm±3 mm) and thetouch-down height (TDH) was examined and, as a result, a strongcorrelation was observed. That is, it was seen that it was possible toreduce the touch-down height (TDH) at the outer peripheral end portionposition by reducing (making approach 1) the ratio (radial directionMW-Rq (OD/MD)) between the microwaviness at the outer peripheral endportion and the microwaviness at the central portion.

Likewise, it was seen that, for example, a tendency (correlation)similar to the above was also observed in the case where two arbitrarypoints at different distances in the radial direction were set asmeasurement regions.

In this invention, the observation of the strong correlation means thatit is possible to prevent large variation in touch-down height (TDH) asshown in FIGS. 15 and 16. In this invention, the observation of thestrong correlation means that it is possible to surely reduce thetouch-down height (TDH) at the outer peripheral end portion position toa predetermined value.

This invention will be explained using an image diagram. Conventionally,as shown at (1) in FIG. 2, the microwaviness at a central portion of adisk is small while the microwaviness at its outer peripheral endportion is relatively large. Herein, as described above, even if themicrowaviness at the outer peripheral end portion is improved (reduced),it is not possible to reduce the touch-down height (TDH) at the outerperipheral end portion position.

On the other hand, the present inventors have found that, as shown at(2) in FIG. 2, even if the microwaviness at a central portion of a diskis relatively large, it is possible to reduce the touch-down height(TDH) over the entire surface of a substrate including its outerperipheral end portion position by providing a surface state where thedifference or ratio between the microwaviness at the central portion andthe microwaviness at the outer peripheral end portion is small.

As a result of further examining the above-mentioned cause, the presentinventors have found that when two regions are arbitrarily selected on asurface of a glass substrate and unless the difference or ratio betweenstandard deviations of microwaviness (definition and so on will bedescribed later) measured in the respective regions satisfies a certainpredetermined relationship, it is not possible to realize a reduction inflying height of a magnetic head.

Specifically, for example, as shown in FIG. 9, the relationship betweenthe difference (circumferential direction MW-Rq STDEV (OD-MD): measuredin a wavelength band of 60 to 500 μm) between a standard deviation ofmicrowaviness at an outer peripheral end portion (e.g. a region alongthe circumferential direction at radius r=31.5 mm±0.05 mm) and astandard deviation of microwaviness at a central portion (e.g. a regionalong the circumferential direction at radius r=25 mm±3 mm) and thetouch-down height (TDH) was examined and, as a result, a strongcorrelation was observed. That is, it was seen that it was possible toreduce the touch-down height (TDH) at the outer peripheral end portionposition by reducing the difference (circumferential direction MW-RqSTDEV (OD-MD)) between the standard deviation of microwaviness in theregion along the circumferential direction at the outer peripheral endportion and the standard deviation of microwaviness in the region alongthe circumferential direction at the central portion.

Further, for example, as shown in FIG. 10, the relationship between theratio (circumferential direction MW-Rq STDEV (OD/MD): measured in awavelength band of 60 to 500 μm) between a standard deviation ofmicrowaviness at an outer peripheral end portion (e.g. a region alongthe circumferential direction at radius r=31.5 mm±0.05 mm) and astandard deviation of microwaviness at a central portion (e.g. a regionalong the circumferential direction at radius r=25 mm±3 mm) and thetouch-down height (TDH) was examined and, as a result, a strongcorrelation was observed. That is, it was seen that it was possible toreduce the touch-down height (TDH) at the outer peripheral end portionposition by reducing (making approach 1) the ratio (circumferentialdirection MW-Rq STDEV (OD/MD)) between the standard deviation ofmicrowaviness in the region along the circumferential direction at theouter peripheral end portion and the standard deviation of microwavinessin the region along the circumferential direction at the centralportion.

Likewise, it was seen that, for example, a tendency (correlation)similar to the above was also observed in the case where two arbitrarypoints at different distances in the radial direction were selected and,with respect to the selected two places, two regions each extendingalong the circumferential direction at the same radius were set asmeasurement regions.

In this invention, the observation of the strong correlation means thatit is possible to prevent large variation in touch-down height (TDH) asshown in FIGS. 15 and 16. In this invention, the observation of thestrong correlation means that it is possible to surely reduce thetouch-down height (TDH) at the outer peripheral end portion position toa predetermined value.

This invention will be explained using an image diagram. Conventionally,as shown at (1) in FIG. 3, the standard deviation of microwaviness at acentral portion of a disk is small while the standard deviation ofmicrowaviness at its outer peripheral end portion is relatively large.

On the other hand, the present inventors have found that, as shown at(2) in FIG. 3, it is possible to reduce the touch-down height (TDH) overthe entire surface of a substrate including its outer peripheral endportion position by providing a surface state where the difference orratio between the standard deviations of microwaviness at its centralportion and its outer peripheral end portion is small.

This invention has found that there is a close relationship on therelationship between the microwaviness on a surface of a substrate andthe glide height (touch-down height (TDH)) and that, by setting themicrowaviness in a predetermined relationship or in a predeterminedrange, it is possible to provide a glass substrate for a magnetic diskcapable of achieving a desired glide height (touch-down height), themagnetic disk, and a method of manufacturing the magnetic disk.

This invention has the following configurations.

(Configuration 1)

A glass substrate for a magnetic disk, wherein, in regions with respectto two places arbitrarily selected on a surface of the glass substrateon a central portion side relative to an outer peripheral end, a surfaceshape with a shape wavelength in a band of 60 to 500 μm is extractedfrom surface shapes in each of the regions and, assuming that a rootmean square roughness Rq of the surface shape is given as amicrowaviness Rq, a difference between the microwavinesses Rq of theregions is 0.02 nm or less.

(Configuration 2)

A glass substrate for a magnetic disk, wherein, in regions with respectto two places arbitrarily selected on a surface of the glass substrateon a central portion side relative to an outer peripheral end, a surfaceshape with a shape wavelength in a band of 60 to 500 μm is extractedfrom surface shapes in each of the regions and, assuming that a rootmean square roughness Rq of the surface shape is given as amicrowaviness Rq, a ratio between the microwavinesses Rq of the regionsis 1.1 or less.

(Configuration 3)

A glass substrate for a magnetic disk according to Configuration 1 or 2,wherein the two places are an outer peripheral end portion of the diskand a central portion of a recording/reproducing area of the disk.

(Configuration 4)

A glass substrate for a magnetic disk according to Configuration 3,wherein the outer peripheral end portion of the disk is a point located1.0 mm inward from an outer peripheral end of the disk toward a centerof the disk or a region located inward of the point.

(Configuration 5)

A glass substrate for a magnetic disk according to Configuration 1 or 2,wherein the regions are two regions each extending along acircumferential direction at the same radius with respect to the twoplaces selected.

(Configuration 6)

A glass substrate for a magnetic disk according to Configuration 1 or 2,wherein an outer peripheral end portion shape of the glass substrate isa shape falling within a range of ±30 nm with respect to a main surfaceas a reference plane.

(Configuration 7)

A glass substrate for a magnetic disk according to Configuration 1 or 2,wherein a touch-down height is 5 nm or less.

(Configuration 8)

A glass substrate for a magnetic disk according to Configuration 1 or 2,wherein the magnetic disk is a magnetic disk for a load/unload system.

(Configuration 9)

A magnetic disk having at least a magnetic layer formed over a surfaceof a glass substrate for a magnetic disk according to Configuration 1 or2.

(Configuration 10)

A magnetic disk manufacturing method, comprising the steps of:

producing a glass substrate for a magnetic disk according toConfiguration 1 or 2, and

forming at least a magnetic layer over a surface of the glass substratefor the magnetic disk.

(Configuration 11)

A glass substrate for a magnetic disk, wherein, in regions with respectto two places arbitrarily selected on a surface of the glass substrateon a central portion side relative to an outer peripheral end, a surfaceshape with a shape wavelength in a band of 60 to 500 μm is extractedfrom surface shapes in each of the regions and, assuming that a rootmean square roughness Rq of the surface shape is given as amicrowaviness Rq, a difference between standard deviations of themicrowavinesses Rq of the regions is 0.04 nm or less.

(Configuration 12)

A glass substrate for a magnetic disk, wherein, in regions with respectto two places arbitrarily selected on a surface of the glass substrateon a central portion side relative to an outer peripheral end, a surfaceshape with a shape wavelength in a band of 60 to 500 μm is extractedfrom surface shapes in each of the regions and, assuming that a rootmean square roughness Rq of the surface shape is given as amicrowaviness Rq, a ratio between standard deviations of themicrowavinesses Rq of the regions is 1.1 or less.

(Configuration 13)

A glass substrate for a magnetic disk according to Configuration 11 or12, wherein the two places are an outer peripheral end portion of thedisk and a central portion of a recording/reproducing area of the disk.

(Configuration 14)

A glass substrate for a magnetic disk according to Configuration 13,wherein the outer peripheral end portion of the disk is a point located1.0 mm inward from an outer peripheral end of the disk toward a centerof the disk or a region located inward of the point.

(Configuration 15)

A glass substrate for a magnetic disk according to Configuration 11 or12, wherein the regions are two regions each extending along acircumferential direction at the same radius with respect to the twoplaces selected.

(Configuration 16)

A glass substrate for a magnetic disk according to Configuration 11 or12, wherein an outer peripheral end portion shape of the glass substrateis a shape falling within a range of ±30 nm with respect to a mainsurface as a reference plane.

(Configuration 17)

A glass substrate for a magnetic disk according to Configuration 11 or12, wherein a touch-down height is 5 nm or less.

(Configuration 18)

A glass substrate for a magnetic disk according to Configuration 11 or12, wherein the magnetic disk is a magnetic disk for a load/unloadsystem.

(Configuration 19)

A magnetic disk having at least a magnetic layer formed over a surfaceof a glass substrate for a magnetic disk according to Configuration 11or 12.

(Configuration 20)

A magnetic disk manufacturing method, comprising the steps of:

producing a glass substrate for a magnetic disk according toConfiguration 11 or 12, and

forming at least a magnetic layer over a surface of the glass substratefor the magnetic disk.

Effect of the Invention

According to this invention, by setting the microwaviness on a surfaceof a substrate in a predetermined relationship or in a predeterminedrange, it is possible to provide a glass substrate for a magnetic diskcapable of achieving a desired glide height (touch-down height), themagnetic disk, and a method of manufacturing the magnetic disk.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary diagram for explaining selected two places andexplaining that use is made of the average value or the standarddeviation of data measured continuously along the circumferentialdirection at the same radius with respect to each of the selected twoplaces.

FIG. 2 is an exemplary diagram for explaining an image of thisinvention.

FIG. 3 is an exemplary diagram for explaining an image of thisinvention.

FIG. 4 is an exemplary diagram for explaining a shape wavelength.

FIG. 5 is an exemplary diagram for explaining Duboff.

FIG. 6 is an exemplary diagram for explaining the structure of aperpendicular magnetic recording disk manufactured in Examples 1 to 5and Comparative Examples 1 to 5.

FIG. 7 is a diagram for explaining that the correlation is observedbetween the difference (MW-Rq (OD-MD)) between microwavinesses in theradial direction and the touch-down height (TDH).

FIG. 8 is a diagram for explaining that the correlation is observedbetween the ratio (MW-Rq (OD/MD)) between microwavinesses (MW-Rq) in theradial direction and the touch-down height (TDH).

FIG. 9 is a diagram for explaining that the correlation is observedbetween the difference (MW-Rq STDEV (OD-MD)) between standard deviationsof microwavinesses in the circumferential direction and the touch-downheight (TDH).

FIG. 10 is a diagram for explaining that the correlation is observedbetween the radio (MW-Rq STDEV (OD/MD)) between standard deviations ofmicrowavinesses in the circumferential direction and the touch-downheight (TDH).

FIG. 11 is a diagram showing the relationship between the difference(MW-Rq (OD-MD)) between microwavinesses in the radial direction and thetouch-down height (TDH) with respect to samples obtained in Examples andComparative Examples.

FIG. 12 is a diagram showing the relationship between the ratio (MW-Rq(OD/MD)) between microwavinesses in the radial direction and thetouch-down height (TDH) with respect to samples obtained in Examples andComparative Examples.

FIG. 13 is a diagram showing the relationship between the difference(MW-Rq STDEV (OD-MD)) between standard deviations of microwavinesses inthe circumferential direction and the touch-down height (TDH) withrespect to samples obtained in Examples and Comparative Examples.

FIG. 14 is a diagram showing the relationship between the ratio (MW-RqSTDEV (OD/MD)) between standard deviations of microwavinesses in thecircumferential direction and the touch-down height (TDH) with respectto samples obtained in Examples and Comparative Examples.

FIG. 15 is a diagram for explaining that no correlation is observedbetween Duboff and the touch-down height (TDH).

FIG. 16 is a diagram for explaining that no correlation is observedbetween the microwaviness (MW-Rq) and the touch-down height (TDH).

FIG. 17 is a diagram for explaining that when the shape wavelength is500 to 1000 μm, the correlation between the difference (MW-Rq (OD-MD))between microwavinesses in the radial direction and the touch-downheight (TDH) is not good.

FIG. 18 is a diagram for explaining that when the shape wavelength is500 to 1000 μm, the correlation between the ratio (MW-Rq (OD/MD))between microwavinesses in the radial direction and the touch-downheight (TDH) is not good.

FIG. 19 is a diagram for explaining that when the shape wavelength is500 to 1000 μm, the correlation between the difference (MW-Rq STDEV(OD-MD)) between standard deviations of microwavinesses in thecircumferential direction and the touch-down height (TDH) is not good.

FIG. 20 is a diagram for explaining that when the shape wavelength is500 to 1000 μm, the correlation between the ratio (MW-Rq STDEV (OD/MD))between standard deviations of microwavinesses in the circumferentialdirection and the touch-down height (TDH) is not good.

FIG. 21 is a diagram for explaining that when the shape wavelength is 10to 60 μm, the correlation between the difference (MW-Rq (OD-MD)) betweenmicrowavinesses in the radial direction and the touch-down height (TDH)is not good.

FIG. 22 is a diagram for explaining that when the shape wavelength is 10to 60 μm, the correlation between the ratio (MW-Rq (OD/MD)) betweenmicrowavinesses in the radial direction and the touch-down height (TDH)is not good.

FIG. 23 is a diagram for explaining that when the shape wavelength is 10to 60 μm, the correlation between the difference (MW-Rq STDEV (OD-MD))between standard deviations of microwavinesses in the circumferentialdirection and the touch-down height (TDH) is not good.

FIG. 24 is a diagram for explaining that when the shape wavelength is 10to 60 μm, the correlation between the ratio (MW-Rq STDEV (OD/MD))between standard deviations of microwavinesses in the circumferentialdirection and the touch-down height (TDH) is not good.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, this invention will be described in detail.

A glass substrate for a magnetic disk according to this invention issuch that, in regions with respect to two places arbitrarily selected ona surface of the glass substrate on its central portion side relative toits outer peripheral end, a surface shape with a shape wavelength in aband of 60 to 500 μm is extracted from surface shapes in each of theregions and, assuming that a root mean square roughness Rq of thesurface shape is given as a microwaviness Rq, a difference between themicrowavinesses Rq of the regions is 0.02 nm or less (Configuration 1).

A glass substrate for a magnetic disk according to this invention issuch that, in regions with respect to two places arbitrarily selected ona surface of the glass substrate on its central portion side relative toits outer peripheral end, a surface shape with a shape wavelength in aband of 60 to 500 μm is extracted from surface shapes in each of theregions and, assuming that a root mean square roughness Rq of thesurface shape is given as a microwaviness Rq, a ratio between themicrowavinesses Rq of the regions is 1.1 or less (Configuration 2).

A glass substrate for a magnetic disk according to this invention issuch that, in regions with respect to two places arbitrarily selected ona surface of the glass substrate on its central portion side relative toits outer peripheral end, a surface shape with a shape wavelength in aband of 60 to 500 μm is extracted from surface shapes in each of theregions and, assuming that a root mean square roughness Rq of thesurface shape is given as a microwaviness Rq, a difference betweenstandard deviations of the microwavinesses Rq of the regions is 0.04 nmor less (Configuration 11).

A glass substrate for a magnetic disk according to this invention issuch that, in regions with respect to two places arbitrarily selected ona surface of the glass substrate on its central portion side relative toits outer peripheral end, a surface shape with a shape wavelength in aband of 60 to 500 μm is extracted from surface shapes in each of theregions and, assuming that a root mean square roughness Rq of thesurface shape is given as a microwaviness Rq, a ratio between standarddeviations of the microwavinesses Rq of the regions is 1.1 or less(Configuration 12).

In this invention, using, for example, a later-described measuringapparatus, a surface shape with a shape wavelength in a band of 60 to500 μm is extracted from surface shapes in a measurement region and amicrowaviness is calculated as a root mean square roughness Rq (RMS) ofthe surface shape. Herein, a measurement length (Q) portion is extractedfrom a roughness curve in a direction of its centerline and, assumingthat the centerline of this extracted portion is represented by theX-axis, that the direction of longitudinal magnification is representedby the Y-axis, and that the roughness curve is expressed by y=f(x),squares of deviations from the centerline to the roughness curve [f(x)]are integrated over the interval of the measurement length (Q) and thenaveraged over that interval to derive an average value. Rq (RMS) is asquare root of this average value. The relationship with Rq (RMS) (rootmean square roughness) prescribed by JIS B 0601 is the same. Therelationship with Wq (root mean square waviness) prescribed by JIS B0601 is the same.

In this invention, a laser Doppler vibrometer (LDV) was used formeasuring the surface state. The measurement principle of this measuringapparatus is that a He—Ne laser beam with a wavelength of 633 nm, forexample, is split into two beams, i.e. a measurement beam and acomparison beam, and the phase difference between the two beams isdetected, thereby measuring the shape of a measurement object based onthat phase difference. A feature of this measuring apparatus is that itis an optical interferometer that irradiates laser light onto an objectand detects the speed based on the frequency difference between theirradiated light and its reflected light. A feature of this measuringapparatus is that it is possible to measure a wide frequency band fromthe surface roughness to the waviness and that it is possible to measurethe entire surface of a disk. The horizontal resolution is about 5 μmand the vertical measurement resolution is 0.001 nm (0.01 Å). Theparameter to be obtained is Rq (RMS).

The laser Doppler vibrometer is exemplified by Optical Process CertifierM4224 manufactured by THoT Technologies, Inc. or the like.

In this invention, as the above-mentioned two places, it is preferableto select two places at different distances from the center of the disk.This is because the correlation appears strongly as compared with thecase where other two places (e.g. in the circumferential direction) areselected.

In this invention, for the above-mentioned two places, the vicinity ofan outer peripheral end portion (excluding an outer peripheral end face,i.e. a substrate side face) of the disk is preferably selected as one ofthe two places and a place considered to show a typical value of arecording/reproducing area (e.g. a central portion of therecording/reproducing area, for example, an intermediate position of aline connecting between inner and outer peripheral ends of the disk) ispreferably selected as the other of the two places (Configurations 3 and13). This is because the correlation appears more strongly as comparedwith the case where other two places are selected.

For example, in the case of a glass substrate for a 2.5-inch magneticdisk with an inner diameter of 20 mm and an outer diameter of 65 mm(inner peripheral end 10 mm and outer peripheral end 32.5 mm measuredfrom a central portion), the vicinity of an outer peripheral end portionof the disk (e.g. a fixed point or a region at a radius 31.5±0.05 mmposition from the center of the substrate) is preferably selected as oneplace and a central portion of a recording/reproducing area (e.g. afixed point or a region at a radius 25 mm±3 mm position from the centerof the substrate) is preferably selected as the other place. The regioncan be a 0.05 to 3 mm square region.

The region in the vicinity of the outer peripheral end portion of thedisk is preferably, for example, a point located 1.0 mm inward from theouter peripheral end of the disk toward the center of the disk or aregion located inward of the point (Configurations 4 and 14) (see FIG.5). This is regardless of the substrate size. This is applicable to, forexample, a 1.8-inch, 2.5-inch, 3.3-inch, or 3.5-inch substrate.

In this invention, it is preferable to use the average value of datameasured along the circumferential direction at the same radius withrespect to each of the selected two places (Configuration 5). This isbecause it is preferable to use the typical value at the positions ofeach radius and the accuracy of correlation is improved thereby.

For example, as shown in FIG. 1, with respect to each of selected twoplaces (A has a width and B is one point), it is preferable to use theaverage value of data measured continuously along the circumferentialdirection at the same radius from the center O of a disk as indicated byimaginary lines.

In this invention, the number of data to be measured continuously alongthe circumference with the same radius can be properly adjusted.

In this invention, it is alternatively possible to intermittently set aplurality of measurement regions at regular intervals along thecircumferential direction at the same radius and to use the averagevalue of data measured in each of the measurement regions.

In this invention, with respect to the selected two places, two regionseach extending along the circumferential direction at the same radiusare set as measurement regions, and it is preferable to use the standarddeviation of data measured in each of the measurement regions(Configuration 15). This is because it is preferable to increase theparameters of the standard deviation and the accuracy of correlation isimproved thereby.

For example, as shown in FIG. 1, with respect to each of selected twoplaces (A has a width and B is one point), it is preferable to use thestandard deviation of data measured continuously along thecircumferential direction at the same radius from the center O of a diskas indicated by imaginary lines.

In this invention, the number of data to be measured continuously alongthe circumference with the same radius can be properly adjusted.

In this invention, it is alternatively possible to intermittently set aplurality of measurement regions at regular intervals along thecircumferential direction at the same radius and to use the standarddeviation of data measured in each of the measurement regions.

In this invention, it is preferable to extract a surface shape with ashape wavelength in a band of 60 to 500 μm from surface shapes in themeasurement region. As shown in FIG. 4, the shape wavelength representsthe distance between adjacent troughs or the distance between adjacentpeaks.

When the shape wavelength is 500 to 1000 μm, the correlation is not goodeven if measured under the same conditions as in FIGS. 7, 8, 9, and 10(see FIGS. 17, 18, 19, and 20).

When the shape wavelength is 10 to 60 μm, the correlation is not goodeven if measured under the same conditions as in FIGS. 7, 8, 9, and 10(see FIGS. 21, 22, 23, and 24).

From the above, it is seen that the upper limit of the shape wavelengthis preferably about half the head size. Therefore, when the head size isreduced in the future, the upper limit of the shape wavelength ispreferably set to about half the head size accordingly.

In this invention, the outer peripheral end portion shape of the glasssubstrate is preferably a shape falling within a range of ±30 nm withrespect to its main surface as a reference plane (Configurations 6 and16).

This is because when Duboff described above is 30 nm or less, the effectof the application of this invention largely appears. Further, this isbecause when Duboff is greater than 30 nm, it is possible to reduce thetouch-down height (TDH) at the outer peripheral end portion position toa certain limit by reducing Duboff.

In this invention, a magnetic head is preferably a magnetic head for aperpendicular magnetic recording medium. In particular, it is preferablya head of the type in which a stylus projects to approach a disk.

In the magnetic disk and its glass substrate according to thisinvention, the average value of the microwaviness (MW-Rq) over theentire surface of the substrate is preferably 4 Å or less.

This is because when the average value of the microwaviness (MW-Rq) is 4Å (0.4 nm) or less, the effect of the application of this inventionlargely appears. Further, this is because when the average value of themicrowaviness (MW-Rq) is greater than 4 Å (0.4 nm), it is not necessaryto apply this invention.

With respect to the magnetic disk and its glass substrate according tothis invention, the touch-down height is preferably 5 nm or less(Configurations 7 and 17).

This is because when the touch-down height is 5 nm or less, the effectof the application of this invention largely appears. Further, this isbecause when the touch-down height is greater than 5 nm, it is notnecessary to apply this invention.

The touch-down height is an index for determining how close a head canapproach a surface of a disk. The touch-down height is measurable usinga film-formed medium (i.e. a magnetic recording medium).

The glide height (flying height) represents the average height of flyingover a substrate. The glide height is a value virtually derived by atester, using a film-formed medium, i.e. a non-transparent object.

Through measurement with the formation of an extremely thin film on asurface of a glass substrate, it is possible to substantially know thesurface state of the glass substrate.

This invention includes the case where the surface state of thefilm-formed medium satisfies the condition defined in Configuration 1,2, 11, or 12 described above.

In the case of an in-plane magnetic recording medium, since thethickness of a magnetic layer and so on is small, it may be consideredthat the surface state of a glass substrate is approximately equal tothat of the film-formed medium. On the other hand, in the case of aperpendicular magnetic recording medium, since the thickness of amagnetic layer and so on is large, the surface state of the film-formedmedium becomes rougher than that of a glass substrate, but since thedegree of roughness caused by the film formation is constant, it may beconsidered that the correlation is achieved before and after the filmformation.

The magnetic disk and its glass substrate according to this inventionare preferably a magnetic disk for a load/unload system and its glasssubstrate (Configurations 8 and 18).

This is because the difference or ratio between the microwavinesses Rqof the respective regions selected with respect to the above-mentionedtwo places particularly becomes a problem in the case of the magneticdisk for the load/unload system and its glass substrate.

The magnetic disk and its glass substrate according to this inventionare preferably a magnetic disk adapted to be mounted in a HDD for use at4,200 rpm or more and its glass substrate (Configurations 9 and 19).

This is because when mounted in the HDD for use at 4,200 rpm or more,the effect of the application of this invention largely appears.

The magnetic disk of this invention has at least a magnetic layer formedover the surface of the glass substrate for the magnetic disk accordingto any of Configurations 1 to 7 described above (Configurations 10 and22).

The magnetic disk and its glass substrate according to this inventionare suitably applicable to a perpendicular magnetic recording medium.

A perpendicular magnetic recording disk has at least a perpendicularmagnetic recording layer over a substrate.

Herein, the perpendicular magnetic recording layer is preferably, forexample, a perpendicular magnetic recording layer having, at least, aferromagnetic layer with a granular structure formed over the substrateand containing an oxide, silicon (Si), or an oxide of silicon (Si) and alaminated layer, on the ferromagnetic layer, of a first layer containingCo or a Co alloy and a second layer containing Pd or Pt.

As a Co-based magnetic material forming the ferromagnetic layer,particularly a CoPt-based or CoPtCr-based magnetic material ispreferable. Si may be added alone or an oxide or a Si oxide such as SiO₂may be added to the CoPt-based or CoPtCr-based magnetic material. Theferromagnetic layer preferably has crystal grains composed mainly of Coand grain boundary portions composed mainly of the oxide, silicon (Si),or the silicon (Si) oxide. The ferromagnetic layer preferably has agranular structure containing Si or its oxide between magnetic crystalgrains containing Co. The thickness of the ferromagnetic layer ispreferably 20 nm or less. Desirably, the range of 8 to 16 nm ispreferable.

The laminated layer is adjacent to the ferromagnetic layer directly orthrough a spacer layer and has a function of magnetically coupling tothe ferromagnetic layer and aligning the easy magnetization axisdirections in the respective layers in approximately the same direction.In the laminated layer, crystal grains are magnetically coupled to eachother. Specifically, with respect to the ferromagnetic layer made of theCo-based magnetic material, the laminated layer preferably comprisesalternately laminated films of cobalt (Co) or its alloy and palladium(Pd) or alternately laminated films of cobalt (Co) or its alloy andplatinum (Pt). Since the alternately laminated films made of suchmaterials have large magnetic Ku, the domain wall width in the laminatedlayer can be made small. The thickness thereof is preferably 1 to 8 nm.Desirably, 2 to 5 nm is preferable. The same effect is obtained even byusing CoCrPt with high Pt content, CoPt, CoPd, FcPt, CoPt₃, or CoPd₃ asa material of the laminated layer, instead of the above-mentionedmultilayer film.

The spacer layer is preferably provided between the ferromagnetic layerand the laminated layer. By providing the spacer layer, it is possibleto suitably control the exchange coupling between the ferromagneticlayer and the laminated layer. As the spacer layer, a Pd layer or a Ptlayer is suitably used depending on the laminated layer, for example.When the Pd layer is used in the laminated layer, the Pd layer is alsoused as the spacer layer. This is because, in terms of the restrictionof a manufacturing apparatus, it is economically preferable to use thesame composition. The thickness of the spacer layer is preferably 2 nmor less and desirably in the range of 0.5 to 1.5 nm.

The ferromagnetic layer and the laminated layer are disposed adjacent toeach other or through the spacer layer therebetween, wherein, in termsof HDI (Head Disk Interface), it is preferable to dispose the laminatedlayer above the ferromagnetic layer as seen from the substrate. Theferromagnetic layer is not limited to a single layer, but may comprise aplurality of layers. In this case, Co-based magnetic layers containingSi or a Si oxide may be combined together or a Co-based magnetic layercontaining Si or a Si oxide and a Co-based magnetic layer not containingSi or a Si oxide may be combined together. It is preferable to disposethe Co-based magnetic layer containing Si or the Si oxide on the sideadjacent to the laminated layer. As a method of forming theperpendicular magnetic recording layer, it is preferable to use asputtering method. In particular, it is preferable to use a DC magnetronsputtering method because uniform film formation is enabled.

The perpendicular magnetic recording disk has at least theabove-mentioned perpendicular magnetic recording layer over thesubstrate and preferably has various functional layers in additionthereto.

For example, a soft magnetic layer for suitably adjusting a magneticcircuit of the perpendicular magnetic recording layer may be providedover the substrate. The soft magnetic layer is not particularly limitedas long as it is made of a magnetic substance that exhibits softmagnetic properties, and, for example, preferably has as its magneticproperty a coercive force (Hc) of 0.01 to 80 oersteds and morepreferably 0.01 to 50 oersteds. Further, it preferably has as itsmagnetic property a saturation magnetic flux density (Bs) of 500 emu/ccto 1920 emu/cc. As a material of the soft magnetic layer, there can becited a Fe-based material, a Co-based material, or the like. Forexample, use can be made of a Fe-based soft magnetic material such asFeTaC-based alloy, FeTaN-based alloy, FeNi-based alloy, FeCoB-basedalloy, or FeCo-based alloy, a Co-based soft magnetic material such asCoTaZr-based alloy or CoNbZr-based alloy, a FeCo-based alloy softmagnetic material, or the like. The thickness of the soft magnetic layeris preferably 30 nm to 1000 nm and desirably 50 nm to 200 nm.

A nonmagnetic underlayer is preferably provided over the substrate fororienting crystals of the perpendicular magnetic recording layer in adirection perpendicular to the surface of the substrate. A Ti-basedalloy is preferable as a material of the nonmagnetic underlayer. TheTi-based alloy well serves to control crystal axes (C-axes) of theCoPt-based perpendicular magnetic recording layer having a hcp crystalstructure to be oriented in the perpendicular direction, which is thuspreferable. As the nonmagnetic underlayer made of the Ti-based alloy,there can be cited, other than Ti, a TiCr-based alloy, a TiCo-basedalloy, or the like. The thickness of such a nonmagnetic underlayer ispreferably 2 nm to 30 nm.

When magnetic field annealing is necessary for controlling magneticdomains of the soft magnetic layer, the substrate is preferably made ofa glass. Since the glass substrate is excellent in heat resistance, theheating temperature of the substrate can be set high. As the glass forthe substrate, there can be cited an aluminosilicate glass, analuminoborosilicate glass, a soda lime glass, or the like. Among them,the aluminosilicate glass is preferable. Further, an amorphous glass ora crystallized glass can be used. When the soft magnetic layer isamorphous, the substrate is preferably made of the amorphous glass. Whena chemically strengthened glass is used, the rigidity is high, which isthus preferable. In this invention, the surface roughness of the mainsurface of the substrate is preferably 6 nm or less in Rmax and 0.6 nmor less in Ra. By providing such a smooth surface, a gap betweenperpendicular magnetic recording layer—soft magnetic layer can be setconstant so that it is possible to form a suitable magnetic circuitbetween magnetic head—perpendicular magnetic recording layer—softmagnetic layer.

It is also preferable to form an adhesive layer between the substrateand the soft magnetic layer. By forming the adhesive layer, the adhesionbetween the substrate and the soft magnetic layer can be improved andtherefore it is possible to prevent stripping of the soft magneticlayer. As a material of the adhesive layer, use can be made of, forexample, a Ti-containing material. In terms of practical use, thethickness of the adhesive layer is preferably set to 1 nm to 50 nm.

In the perpendicular magnetic recording disk, it is preferable toprovide a protective layer on the perpendicular magnetic recordinglayer. By providing the protective layer, it is possible to protect thesurface of the magnetic disk from the magnetic recording head flyingover the magnetic disk. As a material of the protective layer, acarbon-based protective layer, for example, is preferable. The thicknessof the protective layer is preferably about 3 nm to 7 nm.

It is preferable to further provide a lubricating layer on theprotective layer. By providing the lubricating layer, abrasion betweenthe magnetic head and the magnetic disk can be suppressed so that thedurability of the magnetic disk can be improved. As a material of thelubricating layer, PFPE (perfluoropolyether), for example, ispreferable. The thickness of the lubricating layer is preferably about0.5 nm to 1.5 nm.

It is preferable that the soft magnetic layer, the underlayer, theadhesive layer, and the protective layer be also formed by thesputtering method. In particular, the DC magnetron sputtering method ispreferable because uniform film formation is enabled. It is alsopreferable to use an in-line type film forming method. Further, thelubricating layer is preferably formed by, for example, a dip coatingmethod.

The magnetic disk and its glass substrate according to this inventionare also applicable to a discrete-type medium.

A magnetic disk manufacturing method of this invention comprises

a step of producing the glass substrate for the magnetic disk accordingto Configuration 1 or 2 or Configuration 11 or 12 described above, and

a step of forming at least a magnetic layer over the surface of theglass substrate for the magnetic disk (Configurations 10 and 20).

The step of producing the glass substrate for the magnetic diskmanufactures a glass substrate for a magnetic disk having the featuredescribed in Configuration 1, 2, 11, 12, or the like (the feature thatthe difference or ratio between the microwavinesses Rq of the respectiveregions selected with respect to the two places falls in thepredetermined range) in, for example, lapping and polishing processes.

More specifically, the step of manufacturing the glass substrate for themagnetic disk comprises, for example, (1) Rough Lapping Process, (2)Shaping Process, (3) End Face Polishing Process, (4) Precision LappingProcess, (5) First Polishing Process, (6) Second Polishing (FinalPolishing) Process, (7) Cleaning Process, (8) Chemical StrengtheningProcess, (9) Cleaning Process, and (10) Evaluation Process. For example,by controlling the properties of a polishing pad (polishing cloth), thepolishing conditions, and so on in the polishing processes, particularlyby controlling the properties of a polishing pad (polishing cloth), thepolishing conditions, and so on in the second polishing (finalpolishing) process, it is possible to manufacture a glass substrate fora magnetic disk having the above-mentioned feature.

Hereinbelow, Examples and Comparative Examples will be described.

Examples 1 to 5, Comparative Examples 1 to 5

FIG. 6 is an exemplary diagram for explaining the structure of aperpendicular magnetic recording disk manufactured in Examples 1 to 5and Comparative Examples 1 to 5. Hereinbelow, a manufacturing example ofa perpendicular magnetic recording disk will be described with referenceto FIG. 6.

An amorphous aluminosilicate glass was molded into a disk shape bydirect press, thereby producing a glass disk. This glass disk waslapped, polished, and chemically strengthened in sequence, therebyobtaining a smooth nonmagnetic glass substrate 1 in the form of achemically strengthened glass disk. The glass substrate 1 is a 2.5-inchglass substrate with an inner diameter of 20 mm and an outer diameter of65 mm (inner peripheral end 10 mm and outer peripheral end 32.5 mmmeasured from a central portion). The surface roughness of a mainsurface of the glass substrate 1 was measured by an AFM (atomic forcemicroscope) and it was a smooth surface shape with Rmax being 4.8 nm andRa being 0.42 nm. Rmax and Ra follow Japanese Industrial Standard (JIS).

By controlling the properties of a polishing pad, the polishingconditions, and so on in the polishing process, there were manufacturedglass substrates for magnetic disks, each having a value of Duboff, anaverage value of microwaviness (MW-Rq) over the entire surface of thesubstrate, a value of the difference (MW-Rq (OD-MD)) betweenmicrowavinesses in the radial direction, and a value of the ratio (MW-Rq(OD/MD)) between microwavinesses in the radial direction, which areshown in Table 1.

By controlling the properties of a polishing pad, the polishingconditions, and so on in the polishing process, there were manufacturedglass substrates for magnetic disks, each having a value of Duboff, anaverage value of microwaviness (MW-Rq) over the entire surface of thesubstrate, a value of the difference (MW-Rq STDEV (OD-MD)) betweenstandard deviations of microwavinesses in the circumferential direction,and a value of the ratio (MW-Rq STDEV (OD/MD)) between standarddeviations of microwavinesses in the circumferential direction, whichare shown in Table 2.

Then, using an evacuated film forming apparatus, an adhesive layer 2 anda soft magnetic layer 3 were formed in sequence on the obtained glasssubstrate 1 in an Ar atmosphere by the DC magnetron sputtering method.In this event, the adhesive layer 2 was formed by the use of a Ti targetso as to be a Ti layer having a thickness of 20 nm. On the other hand,the soft magnetic layer 3 was formed by the use of a CoTaZr target so asto be an amorphous CoTaZr (Co:88 at %, Ta:7.0 at %, Zr:4.9 at %) layerhaving a thickness of 200 nm.

Then, using an evacuated single-wafer stationary facing type filmforming apparatus, a first underlayer 4a, a second underlayer 4b, aferromagnetic layer 5, a spacer layer 6, a laminated layer 7, and acarbon-based protective layer 8 were formed in sequence on the obtainedsubstrate in an Ar atmosphere by the DC magnetron sputtering method.

Specifically, on the substrate finished with the film formation up tothe soft magnetic layer 3, the first underlayer 4a made of amorphousNiTa (Ni:45 at %, Ta:55 at %) and having a thickness of 10 nm and thesecond underlayer 4b made of Ru and having a thickness of 30 nm werefirst formed. Herein, two layers each made of Ru may be formed instead.That is, by forming the upper-layer side Ru at a gas pressure ofnitrogen (N) gas higher than that used when forming the lower-layer sideRu, the crystal orientation can be improved.

Then, using a hard magnetic target made of CoCrPt containing SiO₂, theferromagnetic layer 5 of 15 nm having a hcp crystal structure wasformed. The composition of the target for forming the ferromagneticlayer 5 was Co:62 at %, Cr:10 at %, Pt:16 at %, SiO₂:12 at %. Theferromagnetic layer 5 was formed at a gas pressure of 30 mTorr. Then,the spacer layer 6 made of Pd and having a thickness of 0.9 nm wasformed. Further, the laminated layer 7 in the form of alternatelylaminated films of CoB and Pd was formed. CoB was first formed into afilm of 0.3 nm and, thereon, Pd was formed into a film of 0.9 nm.Accordingly, the total thickness of the laminated layer 6 was 1.2 nm.The laminated layer 7 was formed at a gas pressure of 10 mTorr lowerthan that used when forming the ferromagnetic layer 5.

Then, using a mixed gas containing 18 vol % hydrogen in Ar, a carbontarget was sputtered, thereby forming the carbon-based protective layer8 made of hydrogenated carbon. The thickness of the carbon-basedprotective layer 8 was 4.5 nm. Since the film hardness is improved inthe form of hydrogenated carbon, it is possible to protect theperpendicular magnetic recording layer against an impact from a magnetichead. Thereafter, a lubricating layer 9 made of PFPE(perfluoropolyether) was formed by the dip coating method. The thicknessof the lubricating layer 9 was 1 nm.

Through the manufacturing processes described above, the perpendicularmagnetic recording disk was obtained. The surface roughness of theobtained perpendicular magnetic recording disk was measured by the AFMin the same manner and it was a smooth surface shape with Rmax being4.53 nm and Ra being 0.40 nm.

(Evaluation)

Tables 1 and 2 and FIGS. 11, 12, 13, and 14 show the results of variousmeasurements of the surfaces of the glass substrates and the magneticdisks thus obtained.

The measurement conditions and so on are as given at (1) to (3) below.

(1) Duboff is measured using a small-size surface roughness measuringapparatus (SURFTEST SJ-624 manufactured by Mitutoyo Corporation) being astylus surface roughness meter. A measurement object is a glasssubstrate (before film formation).

(2) “Microwaviness MW-Rq” is measured using a laser Doppler vibrometer(Optical Process Certifier M4224) manufactured by THoT Technologies,Inc.

Measurement regions are two places, i.e. an outer peripheral end portion(OD: fixed-point observation at a position of radius r=31.5 (±0.05)mm)and a central portion (MD: 1 to 2 mm square regional observation at aposition of radius r=25±3 mm) in the radial direction, and the averagevalue and the standard deviation of data measured continuously along thecircumferential direction at the same radius are derived with respect toeach of the measurement regions (see FIG. 1).

A wavelength band is set to 60 to 500 μm.

A measurement object is a glass substrate (before film formation).

Herein, the measurement conditions of the laser Doppler vibrometermanufactured by THoT Technologies, Inc. are shown in Table 3. Forexample, short wavelength 100 μm and long wavelength 500 μm representthat the measurement is performed in a wavelength band or bandpass of100 to 500 μm.

(3) The touch-down height (TDH) is examined by a touch-down heightevaluation method.

A measurement object is a magnetic disk (after film formation).

In the case of each of the magnetic disks obtained in Examples, thedifference (MW-Rq (OD-MD)) between microwavinesses in the radialdirection was 0.02 nm or less (0.2 Å or less) and the ratio (MW-Rq(OD/MD)) between microwavinesses in the radial direction was 1.1 orless. As a result, the touch-down height (TDH) became 5 nm or less andthus it was applicable as a magnetic disk of 160 G or more.

In the case of each of the magnetic disks obtained in ComparativeExamples, the difference (MW-Rq (OD-MD)) between microwavinesses in theradial direction exceeded 0.02 nm (0.2 Å) and the ratio (MW-Rq (OD/MD))between microwavinesses in the radial direction exceeded 1.1. As aresult, the touch-down height (TDH) exceeded 5 nm and thus it was onlyapplicable as a magnetic disk up to 80 G.

In the case of each of the magnetic disks obtained in Examples, thedifference (MW-Rq STDEV (OD-MD)) between standard deviations ofmicrowavinesses in the circumferential direction was 0.04 nm or less(0.4 Å or less) and the ratio (MW-Rq STDEV (OD/MD)) between standarddeviations of microwavinesses in the circumferential direction was 1.1or less. As a result, the touch-down height (TDH) became 5 nm or lessand thus it was applicable as a magnetic disk of 160 G or more.

In the case of each of the magnetic disks obtained in ComparativeExamples, the difference (MW-Rq STDEV (OD-MD)) between standarddeviations of microwavinesses in the circumferential direction exceeded0.04 nm (0.4 Å) and the ratio (MW-Rq STDEV (OD/MD)) between standarddeviations of microwavinesses in the circumferential direction exceeded1.1. As a result, the touch-down height (TDH) exceeded 5 nm and thus itwas only applicable as a magnetic disk up to 80 G.

TABLE 1 Microwaviness Index of this Invention (MW-Rq) Duboff MW-Rq OD-MDOD/MD TDH Judg- (nm) (Å) (Å) (—) (nm) ment Example 1 10 1.50 0.178 1.084.82 ∘ 2 11 1.43 0.137 1.05 4.55 ∘ 3 12 1.38 0.161 1.07 4.63 ∘ 4 13 1.440.166 1.08 4.67 ∘ 5 15 1.64 0.114 1.05 4.34 ∘ Comparative 1 11 1.380.335 1.17 5.83 x Example 2 11 1.52 0.309 1.14 5.63 x 3 13 1.51 0.2881.14 5.46 x 4 14 1.62 0.323 1.19 5.53 x 5 15 1.57 0.274 1.13 5.44 x ∘:TDH ≦ 5 nm x: TDH > 5 nm

TABLE 2 Microwaviness Index of this Invention (MW-Rq STDEV) Duboff MW-RqOD-MD OD/MD TDH Judg- (nm) (Å) (Å) (—) (nm) ment Example 1 10 1.50 0.0311.09 4.82 ∘ 2 11 1.43 0.027 1.05 4.55 ∘ 3 12 1.38 0.030 1.06 4.63 ∘ 4 131.44 0.031 1.07 4.67 ∘ 5 15 1.64 0.019 1.05 4.34 ∘ Comparative 1 11 1.380.068 1.18 5.83 x Example 2 11 1.52 0.059 1.16 5.63 x 3 13 1.51 0.0511.14 5.46 x 4 14 1.62 0.057 1.16 5.53 x 5 15 1.57 0.051 1.15 5.44 x ∘:TDH ≦ 5 nm x: TDH > 5 nm

TABLE 3 Short Long Spindle Wavelength Wavelength Radius Speed Laser (μm)(μm) (mm) (rpm) Range Micro 100 500 15-31.5 5050 5 Waviness NanoWaviness 60 160 15-31.5 4650 5

While this invention has been described with reference to theembodiment, the technical scope of this invention is not limited to thescope of the description of the above-mentioned embodiment. It isobvious to a person skilled in the art that various changes orimprovements can be added to the above-mentioned embodiment. It is clearfrom the description of claims that the modes added with such changes orimprovements can also be included in the technical scope of thisinvention.

The invention claimed is:
 1. A glass substrate for a magnetic disk,wherein the glass substrate is configured such that, in regions withrespect to two places arbitrarily selected on a surface of the glasssubstrate on a central portion side relative to an outer peripheral end,a surface shape with a shape wavelength in a band of 60 to 500 μm isextracted from surface shapes in each of the regions and, assuming thata root mean square of the surface shape is given as a microwaviness(MW-Rq), a difference between the microwavinesses (MW-Rq) of the regionsis 0.02 nm or less, and a ratio between the microwavinesses (MW-Rq) ofthe regions is 1.1 or less, wherein one of the two places is a regionalong a circumferential direction falling within a range of radius31.5±0.05 mm from a center of the glass substrate while the other placeof the two places is a region along the circumferential directionfalling within a range of radius 25±3 mm from the center of the glasssubstrate, wherein the microwaviness (MW-Rq) is measured using a laserDoppler vibrometer, and wherein an average value of the microwaviness(MW-Rq) on a main surface of the glass substrate is 0.4 nm or less.
 2. Aglass substrate for a magnetic disk according to claim 1, wherein anouter peripheral end portion shape of the glass substrate is a shapefalling within a range of ±30 nm with respect to a main surface as areference plane.
 3. A glass substrate for a magnetic disk according toclaim 1, wherein the glass substrate is for use with a magnetic headhaving a flying height of 5 nm or less.
 4. A glass substrate for amagnetic disk according to claim 1, wherein the magnetic disk is amagnetic disk for a load/unload system.
 5. A magnetic disk having atleast a magnetic layer formed over a surface of a glass substrate for amagnetic disk according to claim
 1. 6. A glass substrate for a magneticdisk according to claim 1, wherein the microwaviness (MW-Rq) at theouter peripheral end is greater than the microwaviness (MW-Rq) on thecentral portion side.
 7. A glass substrate for a magnetic disk accordingto claim 1, wherein an average value and the standard deviation arecalculated for the microwaviness (MW-Rq) measured continuously along thecircumferential direction at the same radius.
 8. A perpendicularmagnetic recording disk, comprising: at least a perpendicular magneticrecording layer formed over the glass substrate according to claim
 1. 9.A glass substrate for a magnetic disk, wherein the glass substrate isconfigured such that, in regions with respect to two places arbitrarilyselected on a surface of the glass substrate on a central portion siderelative to an outer peripheral end, a surface shape with a shapewavelength in a band of 60 to 500 μm is extracted from surface shapes ineach of the regions and, assuming that a root mean square of the surfaceshape is given as a microwaviness (MW-Rq), a difference between standarddeviations of the microwavinesses (MW-Rq) of the regions is 0.04 nm orless, and a ratio between standard deviations of the microwavinesses(MW-Rq) of the regions is 1.1 or less, wherein one of the two places isa region along a circumferential direction falling within a range ofradius 31.5±0.05 mm from a center of the glass substrate while the otherplace the two places is a region along the circumferential directionfalling within a range of radius 25±3 mm from the center of the glasssubstrate, wherein the microwaviness (MW-Rq) is measured using a laserDoppler vibrometer, and wherein an average value of the microwaviness(MW-Rq) on a main surface of the glass substrate is 0.4 nm or less. 10.A glass substrate for a magnetic disk according to claim 9, wherein anouter peripheral end portion shape of the glass substrate is a shapefalling within a range of ±30 nm with respect to a main surface as areference plane.
 11. A glass substrate for a magnetic disk according toclaim 9, wherein the glass substrate is for use with a magnetic headhaving a flying height of 5 nm or less.
 12. A glass substrate for amagnetic disk according to claim 9, wherein the magnetic disk is amagnetic disk for a load/unload system.
 13. A magnetic disk having atleast a magnetic layer formed over a surface of a glass substrate for amagnetic disk according to claim
 9. 14. A glass substrate for a magneticdisk according to claim 9, wherein the microwaviness (MW-Rq) at theouter peripheral end is greater than the microwaviness (MW-Rq) on thecentral portion side.
 15. A glass substrate for a magnetic diskaccording to claim 9, wherein an average value and the standarddeviation are calculated for the microwaviness (MW-Rq) measuredcontinuously along the circumferential direction at the same radius. 16.A perpendicular magnetic recording disk, comprising: at least aperpendicular magnetic recording layer formed over the glass substrateaccording to claim
 9. 17. A glass substrate for a magnetic diskaccording to claim 9, wherein the standard deviations of themicrowaviness (MW-Rq) at the outer peripheral end is greater than thestandard deviations of the microwaviness (MW-Rq) on the central portionside.